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EBSA overview

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The Orange Cone is a transboundary EBSA shared between Namibia and South Africa that spans the mouth of the Orange River: South Africa’s most major river in terms of run-off to the marine environment. It is regionally rare in that comparable habitats are not encountered for 300 km south (Olifants River) and over 1300 km north (Kunene) of this system. The estuary is biodiversity-rich but modified, and the coastal area includes a Critically Endangered habitat type. The pelagic environment has cold waters with high productivity/chlorophyll levels due to upwelling. However, slow, variable currents and weaker winds make it potentially favourable for reproduction of pelagic species, and likely plays a key role in fish recruitment. This EBSA is also a transboundary Ramsar site, and an Important Bird Area.

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Delineation

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Summary of updates and revisions to the EBSA description

R1: 6 new references added; major revisions to the description of the location, feature description of the area, and Criterion 2: importance for life-history stages.

R2: Further editing and formatting throughout the description, with 4 more references added.

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Revised EBSA description

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General Information

Summary

The Orange Cone is a transboundary area between Namibia and South Africa that spans the mouth of South Africa and Namibia’s most major river in terms of run-off to the marine environment. The estuary is biodiversity-rich but modified, and the coastal area includes many Critically Endangered, Endangered, and Vulnerable habitat types (with the area being particularly important for the Critically Endangered Namaqua Sandy Inshore, Namaqua Inshore Hard Grounds and Namaqua Intermediate Sandy Beach habitat types). The marine environment experiences slow, variable currents and weaker winds, making it potentially favourable for reproduction of pelagic species. Further, given the proven importance of river outflow for fish recruitment at the Thukela Banks (a comparable shallow, fine-sediment environment on the South African east coast), a similar ecological dependence for the inshore Orange Cone is likely. Evidence supporting this hypothesis is growing, but has not yet been consolidated. Comparable estuarine/inshore habitats are not encountered for 300 km south (Olifants River) and over 1300 km north (Kunene) of this system. The Orange River Mouth is a transboundary Ramsar site under consideration as a protected area by South Africa and Namibia, and is also an Important Bird Area. Although there are substantial impacted areas especially on the coast and in the estuary, much of the area remains in a natural state. In summary, this area is highly relevant in terms of: ‘Uniqueness or rarity’, ‘Importance for threatened, endangered or declining species and/or habitats’ and ‘Special importance for life history stages of species’.

 

Introduction of the area

The Orange Cone spans the coastal boundary of South Africa and Namibia. The Orange River estuary extends approximately 10 km inland of the sea in a hydrological sense, although estuarine-dependent species migrate much further upstream. The estuary is substantially modified but under rehabilitation. Boundaries of the marine area that is ecologically coupled to the estuary are not accurately known, but could be extensive: seasonally and inter-annually, the marine habitat affected by freshwater outflow varies from a few kilometres to hundreds of kilometres in the longshore direction during floods, particularly southwards (Shillington et al., 1990). This area is located 50 km north and south of the Orange River, extending 30 - 45 km offshore, and includes the full extent of the estuary. Marine and coastal habitat types represented in the area include Namaqua Sandy Inshore, Namaqua Sandy Inner Shelf, Namaqua Inner Shelf, and Namaqua Muddy Inner Shelf habitat types (Sink et al., 2012; Holness et al., 2014). The associated pelagic environment is characterized by upwelling, giving rise to cold waters with high productivity/chlorophyll levels (Lagabrielle 2009). However, the winds in the area are weaker compared to that to the north or south of the area, leading to less local upwelling (Boyd, 1988).

 

Description of the location

EBSA Region

South-Eastern Atlantic

 

Description of location

The Orange River estuary is located at 29°S and forms the boundary between South Africa and Namibia. The Orange Cone is located 50 km north and south of the Orange River, extending 30 – 45 km offshore, and includes the full extent of the estuary. However, the broader area has characteristics of the Orange Cone marine environment as far as 100 km offshore. This EBSA straddles coastal and marine areas within the national jurisdictions of South Africa and Namibia.

 

Area Details

Feature description of the area

Benthic habitat types represented in the area (50 km north and south of the Orange River, extending to approximately 45 km offshore) include Namaqua Sandy Inshore, Namaqua Sandy Inner Shelf and Namaqua Muddy Inner Shelf in South Africa (Sink et al., 2012), and Namaqua Inshore and Namaqua Inner Shelf in Namibia (Holness et al., 2014). The associated pelagic environment is characterized by upwelling, giving rise to cold waters with high productivity/chlorophyll levels (Lagabrielle 2009). However, the winds in the Orange Cone are weaker than those north or south of the area, leading to some stratification (Boyd 1988). Moreover, currents in the inshore region, and indeed over much of the Orange Cone area, have slower velocities and speeds than those occurring further north or south, and movements in both upper and lower layers are dominated by diurnal and/or inertial motions (Iita et al., 2001, Largier and Boyd 2001).

 

The river and estuary have received substantial research attention over the last decade; the adjacent marine environment much less so, apart from some research during the Large Marine Ecosystem (LME) project from 1995-2000. However, given the proven role of the Thukela River outflow for the recruitment of fish stocks in the adjacent marine area on the South African east coast (Turpie and Lamberth 2010), it is hypothesized that the Orange River plays a similar role on the South African west coast. Although not formally described, evidence is mounting to support this hypothesis, because there seem to be many relationships between Orange River flow volumes and demersal, pelagic and nearshore fish biomass (S.J. Lamberth, pers.com, unpublished). For example, the sole fishery collapse was associated with a change in local sediment particle size, because it altered burying difficulty and exposure to predators. Also, anchovy (mostly juveniles) appear to be positively correlated with the size of the plume, because the plume probably serves as a turbidity refuge. Furthermore, the conditions in the area are consistent with the criteria proposed for supporting pelagic species’ reproduction (Parrish et al., 1983).

 

Because of a previous lack of research, the boundaries of the marine zone that is ecologically coupled to the estuary were not accurately known, but were thought to be extensive. For example, geological research suggests that the sediment from the Orange River travels as far north as southern Angola (1750 km north of the mouth), and comprises >80 % of the dune sand along the Skeleton Coast in Namibia (Garzanti et al., 2014). A particular challenge to determining the river’s extent of influence is that the marine habitat affected by freshwater outflow varies greatly both seasonally and inter-annually, from a few to hundreds of kilometres in the longshore direction (mainly southwards) during floods (Shillington et al., 1990). Submarine delta deposits off the mouth of the Orange river extend 26 km offshore, and 112 km alongshore (Rodgers & Rau 2006). The terrigenous material exiting the Orange River has a heterogeneously integrated catchment signal (Hermann et al., 2016) that is generally confined to about 50 km from the shore (Rodgers & Rau 2006). Recent work on marine sediments and delineation of muddy sediment associated habitats have made a far more refined delineation of the Orange Cone possible (Karenyi, 2014; Karenyi et al., 2016), and it is largely these new data which were used to update the Orange Cone EBSA boundaries.

 

In terms of uniqueness of habitat (i.e., refuge for estuarine-dependent or partially dependent fish, and birds), approximately similar estuarine and adjacent inshore habitats are not encountered for over 300 km further south to the Olifants River and over 1300 km further north, until the Kunene River (Lamberth et al., 2008, van Niekerk et al., 2008). The fact that the estuary is a declared Ramsar site (Ramsar 2013) and an Important Bird Area (IBA; BirdLife International 2013) is an important recognition of its importance to birds as well as other species.

 

Feature conditions and future outlook of the proposed area

The impact of reduced and altered flow at the estuary mouth and into the marine environment has had a negative impact on the estuarine habitat, including the salt marsh, which was exacerbated by inappropriate developments associated with mining at the site (van Niekerk and Turpie 2012). The impact of these changes on the marine environment offshore is not known. Both the flow regime (as it will reach the mouth and the marine area) and rehabilitation of the estuary and salt marsh area need to be addressed. However, an estuary management plan is in an advanced stage, and protected area status for the estuary is well advanced as well (van Niekerk and Turpie 2012). Regarding the marine and coastal habitats and biodiversity of the area, the coastline and inshore area to 30 m depth is under considerable threat from mining impacts and is currently unprotected (Sink et al., 2012).

 

Habitat threat status has been estimated in South Africa (Sink et al., 2012) and Namibia (Holness et al., 2014; Table 1) by assessing the (weighted) cumulative impacts of various pressures (e.g., extractive resource use, pollution, development and others) on each habitat type. Key threatened ecosystem types include Namaqua Inshore Hard Grounds, Namaqua Intermediate Sandy Beach and Namaqua Sandy Inshore. Critically Endangered status implies that very little (<= 20%) of the total area of these habitats are in natural/pristine condition, and it is expected that important components of biodiversity pattern have been lost and that ecological processes have been heavily modified. However, within the area, much of these habitat types were assessed to be in ‘fair’ condition. Overall the assessments of Sink et al. (2012) and Holness et al. (2014) classify 79% of the Orange Shelf Edge area as being in good condition, with an additional 12% being in fair condition.

 

References

BirdLife International. 2013. Important Bird Areas: ZA023 Orange River mouth wetlands. URL: www.birdlife.org/datazone/sitefactsheet.php?id=7098 [accessed on 22 April 2013]

Boyd, A. J. 1988. The Oceanography of the Namibian Shelf. PhD Thesis University of Cape Town. 190 pp.

 Currie H., Grobler K., Kemper, J. 2008. Concept note, background document and management proposal for the declaration of Marine Protected Areas on and around the Namibian islands and adjacent coastal areas.

Crawford, R.J.M., Randall, R.M., Whittington, P.A., Waller, L., Dyer, B.M., Allan, D.G., Fox, C., Martin, A.P., Upfold, L., Visagie, J., Bachoo, S., Bowker, M., Downs, C.T., Fox, R., Huisamen, J., Makhado, A.B., Oosthuizen, W.H., Ryan, P.G., Taylor R.H., Turpie, J.K. 2013. South Africa's coastal-breeding white-breasted cormorants: population trends, breeding season and movements, and diet. African Journal of Marine Science, 35: 473-490.

Crawford, R.J.M., Randall, R.M., Cook, T.R., Ryan, P.G., Dyer, B.M., Fox, R., Geldenhuys, D., Huisamen, J., McGeorge, C., Smith, M.K., Upfold, L., Visagie, J., Waller, L.I., Whittington, P.A., Wilke, C.G., Makhado, A.B. 2016. Cape cormorants decrease, move east and adapt foraging strategies following eastward displacement of their main prey. African Journal of Marine Science, 38: 373-383.

Garzanti, E., Vermeesch, P., Andò, S., Lustrino, M., Padoan, M., Vezzoli, G. 2014. Ultra-long distance littoral transport of Orange sand and provenance of the Skeleton Coast Erg (Namibia), Marine Geology 357: 25-36.

Herrmann, N., Boom, A., Carr, A.S., Chase, B.M., Granger, R., Hahn, A., Zabel, M., Schefuß, E. 2016. Sources, transport and deposition of terrestrial organic material: A case study from southwestern Africa. Quaternary Science Reviews, 149: 215-229.

Holness S., Kirkman S., Samaai T., Wolf T., Sink K., Majiedt P., Nsiangango S., Kainge P., Kilongo K., Kathena J., Harris L., Lagabrielle E., Kirchner C., Chalmers R., Lombard M. 2014. Spatial Biodiversity Assessment and Spatial Management, including Marine Protected Areas. Final report for the Benguela Current Commission project BEH 09-01.

Hutchings, L., Beckley, L.E., Griffiths, M.H., Roberts, M.J., Sundby, S., van der Lingen, C. 2002. Spawning on the edge: spawning grounds and nursery areas around the southern African coastline. Marine and Freshwater Research 53: 307-318.

Iita, A., Boyd, A.J., Bartholomae, C.H. 2001. A snapshot of the circulation and hydrology of the southern and central shelf regions of the Benguela Current in winter 1999. South African Journal of Science, 97: 213–217.

Jansen, T., Kristensen, K., Kainge, P., Durholtz, D., Strømme, T., Thygesen, U.H., Wilhelm, M.R., Kathena, J., Fairweather, T.P., Paulus, S., Degel, H., Lipinski, M.R., Beyer, J.E. 2016. Migration, distribution and population (stock) structure of shallow-water hake (Merluccius capensis) in the Benguela Current Large Marine Ecosystem inferred using a geostatistical population model. Fisheries Research, 179: 156–167.

Karenyi, N. 2014. Patterns and Drivers of Benthic Macrofauna to Support Systematic Conservation Planning for Marine Unconsolidated Sediment. Nelson Mandela Metropolitan University, Port Elizabeth.

Karenyi, N., Sink, K., Nel, R. 2016. Defining seascapes for marine unconsolidated shelf sediments in an eastern boundary upwelling region: The southern Benguela as a case study. Estuarine, Coastal and Shelf Science, 169: 195-206.

Lagabrielle E. 2009. Preliminary report: National Pelagic Bioregionalisation of South Africa. Cape Town: South African National Biodiversity Institute.

Lamberth, S.J., Van Niekerk, L., Hutchings, K. 2008. Comparison of, and the effects of altered freshwater inflow on, fish assemblages of two contrasting South African estuaries: the cool-temperate Olifants and the warm-temperate Breede. African Journal of Science, 30: 331–336.

Mann BQ. 2000. Status Reports for Key Linefish Species. Durban: Oceanographic Research Institute Special Publication

Parrish, R.H., A. Bakun, D.M. Husby, and C.S. Nelson. 1983. Comparative climatology of selected environmental processes in relation to eastern boundary current pelagic fish reproduction. p. 731-778. In: G.D. Sharp and J. Csirke (eds.) Proceedings of the Expert Consultation to Examine Changes in Abundance and Species Composition of Neritic Fish Resources. FAO Fish. Rep. 291(3), 1224 pp.

Ramsar. 2013. Orange River Mouth, Ramsar site no. 526. The annotated Ramsar list: South Africa. URL: www.ramsar.org/cda/en/ramsar-documents-list-anno-southafrica/main/ramsar [accessed on 22 April 2013]

Rodgers, J., Rau, A.J. 2006. Surficial sediments of the wave-dominated Orange River Delta and the adjacent continental margin off south-western Africa. African Journal of Marine Science, 28: 511-524.

Shillington, F.A., Brundrit, G.B., Lutjeharms, J.R.E., Boyd, A.J., Agenbag, J.J., Shannon, L.V. 1990. The coastal current circulation during the Orange River flood 1988. Transaction of the Royal Society of South Africa, 47: 308-329.

Sink, K., Holness, S., Harris, L., Majiedt, P., Atkinson, L., Robinson, T., Kirkman, S., Hutchings, L., Leslie, R., Lamberth, S., Kerwath, S., von der Heyden, S., Lombard, A., Attwood, C., Branch, G., Fairweather, T., Taljaard, S., Weerts, S., Cowley, P., Awad, A., Halpern, B., Grantham, H., Wolf, T. 2012. National Biodiversity Assessment 2011: Technical Report. Volume 4: Marine and Coastal Component. South African National Biodiversity Institute, Pretoria.

Turpie, J., Lamberth, S.J. 2010. Characteristics and value of the Thukela Banks crustacean and linefish fisheries, and the potential impacts of changes in river flow. African Journal of Marine Science, 32: 613-624.

van Niekerk, L., Neto, D.S., Boyd, A.J., Holtzhausen, H. 2008. BCLME Project BEHP/BAC/03/04: Baseline Surveying of Species and Biodiversity in Estuarine Habitats. Benguela Environment Fisheries Interaction & Training Programme and Instituto Nacional de Investigacao Pesqueira. 152 pp.

Van Niekerk, L. and Turpie, J.K. (eds). 2012. South African National Biodiversity Assessment 2011: Technical Report. Volume 3: Estuary Component. CSIR Report Number CSIR/NRE/ECOS/ER/2011/0045/B. Council for Scientific and Industrial Research, Stellenbosch.

 

Other relevant website address or attached documents

Table 1: Summary of ecosystem types and threat status for the Orange Cone Data from Sink et al., 2012 and Holness et al., 2014.

Ecosystem Threat Status

Ecosystem Type

Area (km2)

Area (%)

Critically Endangered

Namaqua Inshore Hard Grounds

22.9

0.7

 

Namaqua Inshore Reef

0.5

0.0

 

Namaqua Intermediate Sandy Beach

29.7

1.0

 

Namaqua Reflective Sandy Beach

3.1

0.1

 

Namaqua Sandy Inshore

144.4

4.7

Critically Endangered Total

 

200.6

6.5

Endangered

Namaqua Mixed Shore

3.8

0.1

Endangered Total

 

3.8

0.1

Vulnerable

Namaqua Inshore

323.0

10.5

 

Namaqua Very Exposed Rocky Coast

1.5

0.0

Vulnerable Total

 

324.6

10.5

Least Threatened

Namaqua Estuarine Shore

4.3

0.1

 

Namaqua Exposed Rocky Coast

10.8

0.4

 

Namaqua Hard Inner Shelf

7.3

0.2

 

Namaqua Inner Shelf

1560.6

50.5

 

Namaqua Muddy Inner Shelf

645.3

20.9

 

Namaqua Sandy Inner Shelf

321.5

10.4

 

Southern Benguela Dissipative Sandy Coast

4.7

0.2

 

Southern Benguela Dissipative-Intermediate Sandy Coast

0.2

0.0

 

Southern Benguela Estuarine Shore

2.2

0.1

 

Southern Benguela Intermediate Sandy Coast

1.1

0.0

 

Southern Benguela Reflective Sandy Coast

1.5

0.0

Least Threatened Total

 

2559.6

82.9

Grand Total

 

3088.6

100.0

 

Status of submission

Areas described as meeting EBSA criteria that were considered by the Conference of the Parties

 

COP Decision

dec-COP-12-DEC-22

 

Assessment of the area against CBD EBSA criteria

C1: Uniqueness or rarity High

Justification

In terms of uniqueness of habitat (i.e., refuge for estuarine-dependent or partially estuarine-dependent fish and birds), approximately similar estuarine and adjacent inshore habitat are not encountered for over 300 km further south to the Olifants River, and over 1300 km further north, until the Kunene River (van Niekerk et al., 2008, Lamberth et al., 2008). The marine area is fed by the estuarine outflow, and also has its own oceanographic characteristics in terms of inertial currents and stratification, thus being largely “sheltered” from Benguela System forcing (Boyd 1988, Largier and Boyd 2001).

 

C2: Special importance for life-history stages of species High

Justification

A total of 33 fish species from 17 families have been captured from the Orange River estuary (van Niekerk et al., 2008). Thirty four percent showed some degree of estuarine dependence, 24 % were marine and the remaining 42 % were freshwater species. The high diversity and abundance of estuarine-dependant and marine species suggests that this is an extremely important estuarine nursery area, especially for Kob species (van Niekerk and Turpie 2012), and not just a freshwater conduit as previously thought (van Niekerk et al., 2008). Certainly, oceanographic conditions in the area are consistent with the criteria proposed by Parrish et al. (1983) for the reproduction of pelagic species, and the system is also hypothesised to play a similar role to that of the comparable Thukela River/Thukela Banks (on the South African east coast) where the freshwater outflow is proven to support recruitment of fish stocks (Turpie and Lamberth 2010). Evidence is continually mounting to confirm the role of the Orange Cone in supporting key life-history stages. For example, the area is the northern margin of the important west coast nursery ground for pelagic fish species with periodic spawning (Hutchings et al., 2002). The Orange Cone is also an important recruitment/nursery area and one of three primary population components for shallow water hake (Jansen et al., 2016). Further, northern sections of the Orange Cone, particularly the coastal reef, are called “Mittag”, and are important for the Namibian commercial rock lobster fishery (Currie et al., 2008). The estuary area is also an important stopover site for migrating shorebirds and other waterbirds, and provides breeding habitat for birds such as White-breasted Cormorants (Crawford et al., 2013) and Cape Cormorants. However, there have been fewer individuals of the latter species breeding in recent years (Crawford et al., 2016).

 

South of the Kunene River (over 1300 km to the north of the Orange River), the only permanently open estuaries on the west coast of the subregion include the Orange, Olifants and Berg Rivers (Lamberth et al., 2008). Migration up and down the west coast of southern Africa by marine and estuarine species, e.g., Angolan dusky kob, and west coast steenbras, may be dependent on the availability of warm water refugia offered by these estuary mouths and their plumes, especially during upwelling months (Lamberth et al., 2008).

 

C3: Importance for threatened, endangered or declining species and/or habitats High

Justification

Five of the inshore habitat types (Namaqua Inshore Hard Grounds, Namaqua Inshore Reef, Namaqua Intermediate Sandy Beach, Namaqua Reflective Sandy Beach, Namaqua Sandy Inshore) found in the Orange Cone are Critically Endangered, indicating that very little (< 20%) of the remaining area of this habitat is in good (natural or pristine) condition (Sink et al., 2012; Holness et al., 2014). In addition, these studies identified one Endangered (Namaqua Mixed Shore) and two Vulnerable ecosystem types (Namaqua Inshore, Namaqua Very Exposed Rocky Coast) that are represented in the EBSA. Although these habitats are highly impacted across their range, their local condition in the Orange Cone is largely ‘good’ or ‘fair’ (Sink et al., 2012; Holness et al., 2014), though the coastal types are heavily impacted. The area is also an important nursery for coastal fish species, such as kob (van Niekerk and Turpie 2012) which are overexploited (Mann 2000). The estuary includes important breeding habitat for Endangered Cape Cormorants (Crawford et al., 2016).

 

C4: Vulnerability, fragility, sensitivity, or slow recovery Medium

Justification

The estuarine salt marsh area is vulnerable and has been slow to show recovery despite rehabilitation efforts (van Niekerk and Turpie 2012). There has also been a marked decline in certain fish stocks that were previously exploited in the region (Lamberth et al., 2008). Mining and habitat modification are thought to have had an impact with respect to these changes.

 

C5: Biological productivity Medium

Justification

Winds in the Orange Cone are weaker than those which occur to the north or south of the area, leading to some stratification (Boyd 1988). This, and the effect of the fresh water inflow, may serve to concentrate productivity.

 

C6: Biological diversity Medium

Justification

A high diversity of fish species (33 species from 17 families) has been captured from the Orange River estuary (van Niekerk et al., 2008), including freshwater, marine and estuarine-dependent species. The marine area served as the conduit supporting the estuary’s biodiversity for migratory marine and estuarine-dependent species, as well as marine pelagic and demersal species, including their juvenile stages. Further, the fact that the estuary is a declared Ramsar site (Ramsar 2013) and an IBA (BirdLife International 2013) is an important recognition of its importance to birds and other species.

 

C7: Naturalness Medium

Justification

The estuary and nearshore are impacted, but the estuary still provides many ecological services such as recruitment. The shelf and inshore habitats are still in good or fair condition, although there are significant impacts from coastal diamond mining in Namibia and to a lesser extent in South Africa (Sink et al., 2012; Holness et al., 2014). Though data are sparse, the inner shelf area is largely in good condition (Sink et al., 2012; Holness et al., 2014), but there have been long-term declines in fish catch. 

 

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